The present invention relates to infectious diseases and, more particularly, to chimeric protein vaccines and methods of use thereof in the treatment of Staphylococcus aureus. 
Staphylococcus aureus (S. aureus) is a common cause of hospital-acquired infections and represents an important public health threat. S. aureus can cause nosocomial (hospital) and community-acquired infections including impetigo, cellulitis, food poisoning, toxic shock syndrome, invasive necrotizing pneumonia, and endocarditis. S. aureus is also the most common species of staphylococci to cause Staph infections. Currently, it is one of the top causes of infectious disease deaths in the United States.
S. aureus also causes mastitis, which is a major problem in dairy cows with considerable economic implications. For example, mastitis in dairy cows is most commonly caused by S. aureus and is one of the most common diseases infecting dairy cattle in the United States. S. aureus causes a persistent, inflammatory reaction of the udder tissue that can lead to chronic infections that result in the cow being culled from the herd. Milk from cows with mastitis also typically have higher somatic cell count, which generally lowers the milk quality. It is estimated that mastitis may cost the dairy industry billions of dollars per year in economic losses.
A growing concern in the treatment of S. aureus is that the bacterium is often resistant to multiple antibiotics. Roughly half of the nosocomial isolates in the United States are methicillin-resistant S. aureus (MRSA). Methicillin-resistant S. aureus is also sometimes referred to as “multidrug-resistant” S. aureus or “oxacillin-resistant S. aureus.” MRSA bacterium is generally resistant to beta-lactam antibiotics, which include the penicillins (e.g., methicillin, dicloxacillin, nafcillin, oxacillin, etc.) and cephalosporins. Currently, a vaccine that prevents staphylococcal disease is unavailable.
A possible approach for staphylococcal vaccine development is to target virulence factors such as toxins, enzymes, polysaccharide capsules, adhesive factors, and the like. A key to the possible vaccine approach may be that the anterior nares of humans are known to be an important niche for S. aureus. It is believed that nasal carriage is a major risk factor for invasive infection.
One potential S. aureus virulence factor is the iron-regulated surface determinant A (IsdA). IsdA is an S. aureus surface adhesin protein that may be immunogenic in certain organisms. IsdA can bind to human desquamated nasal epithelial cells and is believed to play a critical role in nasal colonization.
However, a major obstacle in vaccine development of S. aureus is the lack of immunostimulatory adjuvants that can function from mucosal surfaces. While certain toxins (e.g., cholera toxin and heat-labile toxin) have the ability to induce mucosal and systemic immune responses to co-administered antigens, these bacterial proteins are generally too toxic for human use.